//-----------------------------------------------------------------------------
//
// Copyright (C) Microsoft Corporation.  All Rights Reserved.
//
//-----------------------------------------------------------------------------
using System;
using System.Diagnostics.Contracts;

// Visitor to search for types proxies that could not completely be
// determined by type inference. If this happens, a warning is
// generated and the proxies are instantiated in a more or less arbitrary
// fashion.

namespace Microsoft.Boogie {

  public class TypeAmbiguitySeeker : StandardVisitor {

    private readonly InTypeSeeker/*!*/ inTypeSeeker = new InTypeSeeker();
    private readonly TypecheckingContext/*!*/ TC;
    [ContractInvariantMethod]
    void ObjectInvariant() {
      Contract.Invariant(inTypeSeeker != null);
      Contract.Invariant(TC != null);
    }


    public TypeAmbiguitySeeker(TypecheckingContext tc) {
      Contract.Requires(tc != null);
      TC = tc;
    }

    private void CheckTypeParams(Absy node, TypeParamInstantiation insts) {
      Contract.Requires(insts != null);
      Contract.Requires(node != null);
      foreach (TypeVariable/*!*/ var in insts.FormalTypeParams) {
        Contract.Assert(var != null);
        Type/*!*/ inst = insts[var];
        Contract.Assert(inst != null);

        inTypeSeeker.FoundAmbiguity = false;
        inTypeSeeker.Visit(inst);
        if (inTypeSeeker.FoundAmbiguity)
          TC.Warning(node,
                     "type parameter {0} is ambiguous, instantiating to {1}",
                     var, inst);
      }
    }

    public override Expr VisitNAryExpr(NAryExpr node) {
      //Contract.Requires(node != null);
      Contract.Ensures(Contract.Result<Expr>() != null);
      CheckTypeParams(node, cce.NonNull(node.TypeParameters));
      return base.VisitNAryExpr(node);
    }

    public override AssignLhs VisitMapAssignLhs(MapAssignLhs node) {
      //Contract.Requires(node != null);
      Contract.Ensures(Contract.Result<AssignLhs>() != null);
      CheckTypeParams(node, cce.NonNull(node.TypeParameters));
      return base.VisitMapAssignLhs(node);
    }
  }

  internal class InTypeSeeker : StandardVisitor {

    internal bool FoundAmbiguity = false;

    // called when an uninstantiated proxy was found
    private Type Instantiate(Type node, Type inst) {
      Contract.Requires(inst != null);
      Contract.Requires(node != null);
      Contract.Ensures(Contract.Result<Type>() != null);
      FoundAmbiguity = true;
      bool success = node.Unify(inst);
      Contract.Assert(success);
      return node;
    }

    public override Type VisitTypeProxy(TypeProxy node) {
      //Contract.Requires(node != null);
      Contract.Ensures(Contract.Result<Type>() != null);
      if (node.ProxyFor != null)
        return base.VisitTypeProxy(node);

      return Instantiate(node, Type.Int);
    }

    public override Type VisitMapTypeProxy(MapTypeProxy node) {
      //Contract.Requires(node != null);
      Contract.Ensures(Contract.Result<Type>() != null);
      if (node.ProxyFor != null)
        return base.VisitMapTypeProxy(node);

      TypeVariableSeq/*!*/ typeParams = new TypeVariableSeq();
      TypeSeq/*!*/ arguments = new TypeSeq();
      for (int i = 0; i < node.Arity; ++i) {
        TypeVariable/*!*/ param = new TypeVariable(Token.NoToken, "arg" + i);
        Contract.Assert(param != null);
        typeParams.Add(param);
        arguments.Add(param);
      }
      TypeVariable/*!*/ result = new TypeVariable(Token.NoToken, "res");
      Contract.Assert(result != null);
      typeParams.Add(result);

      Type/*!*/ instantiation = new MapType(Token.NoToken, typeParams, arguments, result);
      Contract.Assert(instantiation != null);

      return Instantiate(node, instantiation);
    }

    public override Type VisitBvTypeProxy(BvTypeProxy node) {
      //Contract.Requires(node != null);
      Contract.Ensures(Contract.Result<Type>() != null);
      if (node.ProxyFor != null)
        return base.VisitBvTypeProxy(node);

      return Instantiate(node, new BvType(node.MinBits));
    }
  }

}